At present, physicians can view internal regions of the body using well known ultrasonic imaging techniques. Procedures, for example, which utilize ultrasonic imaging techniques, include the biopsy of potentially malignant tumors. The biopsy procedure utilizes an interventional medical device, such as a biopsy needle, which the physician inserts into the body of a patient. The physician guides the biopsy needle toward the tissue to be biopsied by watching an image of an internal region of the body produced by the ultrasonic imaging system. During this procedure, it is supremely important for the physician to be able to clearly visualize the needle while guiding it through the patient's body toward the area of tissue to be removed by the biopsy needle, as the needle can bend off the intended path and pierce vital organs.
Ultrasonic imaging techniques may also be used in other procedures to monitor the placement of other types of medical instruments including trocars, catheters, etc., within the body.
The prior art includes a number of methods for monitoring the path of medical devices as they are directed through the body of a patient. For example, the insertion path of a catheter can be monitored using ultrasonic imaging techniques. In U.S. Patent No. 4,497,595 issued to Breyer et al., a cardiac catheter and its associated pacing leads, which carry one or more ultrasonic transducers, are used in combination with an ultrasonic imaging system. The catheter or the leads are represented inside the body as an ultrasonic image by reception or transmission of ultrasonic signals between the imaging transducer and the transducer mounted on the pacing leads. Another method is found in U.S. Pat. No. 5,076,278 issued to Vilkomerson et al. The '278 patent discloses an annular ultrasonic transducer that is sensitive over a broad range of angles of incident acoustic beams and which is mounted on a catheter or other medical device. By utilizing an ultrasonic imaging system, the position of the transducer on the catheter during ultrasonic scanning modes can be ascertained and incorporated into the image generated by the imaging system. This system, however, detects and displays only one point of the medical device.
Biopsy needles can also be monitored within the body using ultrasonic imaging techniques by providing the needle with an ultrasonic transducer in order to cause the needle to transmit and/or receive ultrasonic waves in cooperation with an imaging scanhead. For example, U.S. Pat. No. 3,556,079 issued to Omizo discloses a method whereby Doppler interrogating waves are directed forward from the tip of a biopsy needle. As the needle penetrates the body, backscatter waves from moving fluids within a vessel or organ are received and a conventional Doppler beat frequency is detected. The reception of the Doppler tone provides an indication that the needle is aimed at the vessel or organ containing the fluid. The Omizo method is a highly directional method and consequently, if the needle becomes misdirected, no backscatter waves will be returned thereby causing the Doppler tone to cease.
More recently in U.S. Pat. No. 4,249,539 issued to Vilkomerson et al., a system is disclosed which includes an omnidirectional transducer located at the needle tip. The transducer is used as a transponder to send signals back through the body to a transmitter when a signal is detected. The omnidirectional transducer exchanges ultrasonic waves with the imaging transducer irrespective of the orientation of the omnidirectional transducer, thus enabling the system to continually provide a visual marker in the ultrasonic image which indicates the needle tip location. An ultrasonic imaging transducer provides a two-dimensional image as it scans a relatively planar portion of the patient's body. Consequently, the needle tip can only be visualized when it is located within the scan plane of the imaging transducer. Hence, the '539 system cannot visualize the needle tip when the physician first enters the body if the plane of penetration is outside of the scan plane of the imaging transducer. When this occurs, the physician is required to focus his attention on the insertion and guidance of the biopsy needle and at the same time manipulate the imaging transducer and watch the imaging monitor to simultaneously orient the transducer and the needle so that the tissue structure to be biopsied and the needle tip are in the image or scan plane.
Most recently in U.S. Pat. No. 5,095,910 issued to Powers, a biopsy needle with a reciprocating tip that produces a highly directional motion is described. The highly directional motion produces a Doppler shift which is detected and displayed by a color ultrasonic imaging system. As a result, the needle tip can be monitored as it is guided toward the tissue to be biopsied. The biopsy needle in the '910 patent comprises an inner solid element or stylet which reciprocates longitudinally within a hollow tube or cannula. The only motion that appears in the ultrasonic colorflow image as a visual Doppler response is the motion of the tip of the stylet at the open end of the cannula. This motion is shown as color. The system will not show the tip of the stylet if the tissue is liquid in nature, such as in the necrotic center of tumors, or when the stylet tip is at right angles to the ultrasound beam. The reciprocating motion is provided by a driver in the hub of the needle. As such, this arrangement is limited to specially prepared needles or other such devices for use in this system.
It should also be mentioned that color imaging has also been utilized in ultrasound systems used to measure blood velocity. The prior art recognizes that moving blood cell reflect ultrasonic energy that is Doppler shifted in frequency. Therefore, the velocity of the blood may be measured by utilizing an ultrasound imaging system. Moreover, ultrasound imaging systems have been utilized to locate the best point in a blood vessel in which to measure blood velocity by measurement of the Doppler shift. The Doppler shift in backscattered ultrasound at a point in a blood vessel is measured by the detection of quadrature time samples of the backscattered signal. This technique entails the monodyne detection of the signal in conjunction with sine and cosine mixing at a transmitted frequency in order to detect real and imaginary parts of a signal vector at a sampling time. The signal vector, which is a sum of the individual signal vectors from each blood cell, changes slowly (assuming the blood cells stay in the same relative positions) but advances or retreats in phase depending upon whether the blood cells are coming toward a transducer or away.
In copending Patent application Ser. No. 08/022112, the disclosure of which is expressly incorporated herein by reference, the applicants describe a system in which the tip of a biopsy needle or other interventional medical device is visualized in the body of a patient using a color ultrasonic imaging system. Disclosed therein is an apparatus and method for causing a periodic or oscillating mechanical motion in the needle which results in a significant Doppler shift effect that enables the needle to be detected by the color ultrasonic imaging system. The needle or other interventional medical device is made to oscillate by a mechanical motion mechanism. The needle is coupled and secured to the mechanical motion mechanism using a flexible clip-like element formed for instance, from any suitable metal or plastic. The flexible clip-like element is designed to accommodate and secure needles of different gages to the mechanical motion mechanism. Current medical practice dictates the use of needles having gages ranging from 14 gage (2.0 mm in diameter) to 25 gage (0.4 mm in diameter). Problems, however, having to do with assured firm fixation of the needle to the mechanical motion mechanism still arise due to the fixed diameter of the flexible clip-like element. The selected diameter of the clip-like element results in a compromise which tends to favor needles in a given narrow gage range. Needle sizes falling at the outer ends of this range tend to fit less securely than needle sizes which fall within the given narrow range. Consequently, in cases where the needle fits less securely the mechanical motion transfer from the mechanical motion device to the needle results in ineffective operation of the imaging system.
It is therefore an object of the present invention to provide a method for firmly and consistently attaching needles of varying diameters to a mechanical motion mechanism used in a color ultrasonic imaging system which utilizes a lock having a fixed diameter.